A radio system comprising a transmitter is susceptible to a form of interference called intermodulation (IM). IM can be generated when non-linear parts or elements of a transmitter output, often the power amplifier output stages, mix the intended output of the transmitter with an interfering signal. The resultant IM or IM product can reduce the performance of a communication system by lowering the signal to noise ratio in the intended output and creating an IM signal that results in interference for an adjacent or near channel.
One form of IM results when a desired output signal from a transmitter is mixed with an interfering signal reversed coupled from the antenna that is intended to radiate the desired output signal or transmitter signal. Decreasing the amount or amplitude of the interfering signal that is coupled to the transmitter output can reduce this form of IM. This reduction is often done with circulators and isolators, however circulators and isolators have limited effectiveness. A need exists for a method and apparatus for reducing interfering signals in a transmitter.